The liquid crystal display device is a flat display device having excellent features, such as high definition, thin shape, light weight, and low power consumption, and is widely used for a flat TV, a PC monitor, a digital signage, and the like.
A twisted nematic (TN) mode liquid crystal display device that has been conventionally used in general is excellent in productivity, but has a problem in viewing angle characteristics relevant to screen display. For example, when the display screen is viewed from an oblique direction with respect to the normal line, the contrast ratio is significantly reduced and the brightness difference between gradations is significantly unclear in the TN mode liquid crystal display device. In addition, a so-called gradation inversion phenomenon may be observed in which a portion that looks bright (or dark) when the display screen is viewed from the front looks dark (or bright) when the display screen is viewed from an oblique direction with respect to the normal line.
As liquid crystal display devices for solving the problem of the viewing angle characteristics described above, there are liquid crystal display devices that perform display in display modes, such as an in-plan switching (IPS) mode and a multi domain vertical alignment (MVA) mode. Techniques for realizing the display modes in these liquid crystal display devices are widely used as techniques for improving the viewing angle characteristics.
Incidentally, one of problems of the viewing angle characteristics is that the gamma characteristics indicating the gradation dependence of the display brightness depend on the angle of the line of sight with respect to the normal line of the display screen (hereinafter, referred to as the viewing angle dependence of the gamma characteristics). This problem is that the gradation display state differs depending on the observation direction with respect to the display screen and accordingly the gamma characteristics are differently observed between a case where the observation direction is a direction along the normal line of the display screen and a case where the observation direction is an oblique direction with respect to the normal line of the display screen.
On the other hand, Non-Patent Document 1 (Sang Soo Kim, Bong Hyun You, Jung Hwan Cho, Sung Jae Moon, Brian H. Berkeley and Nam Deog Kim, ‘82″ Ultra Definition LCD Using New Driving Scheme and Advanced Super PVA Technology’, SID Symposium Digest of Technical Papers, May 2008, Volume 39, Issue1, p. 196-199) discloses a liquid crystal display device for improving the viewing angle dependence (referred to as viewing angle dependence in some documents) of the gamma characteristics. In the liquid crystal display device disclosed in Non-Patent Document 1, each pixel is configured to include first and second subpixels, and a discharge capacitor (Cdown) is provided in the second subpixel. Subpixel electrodes of the first and second subpixels are connected to data signal lines (source signal lines), which are different alternately for respective pixels in the vertical direction of the display screen, through TFT1 and TFT2 having control electrodes to which a scanning signal (gate signal) is applied from the scanning signal line, and two lines are simultaneously scanned. In the discharge capacitor, a discharge capacitor electrode facing a counter electrode is connected to the subpixel electrode of the second subpixel through a TFT3. In addition, a discharge signal line for applying a discharge signal to the control electrode of the TFT3 is connected to the scanning signal line behind two lines.
In the liquid crystal display device disclosed in Non-Patent Document 1, for each pixel, a discharge signal delayed by one horizontal scanning period (1 H) from the scanning signal for each pixel is applied to the control electrode of the TFT3. By connecting the discharge capacitor electrode and the subpixel electrode of the second subpixel according to the signal delayed by 1 H from the scanning signal in this manner, the effective voltage applied to the liquid crystal layer by each of the first and second subpixels can be changed. In this case, since each pixel is observed in a state in which the gamma characteristics that are different for respective subpixels are harmonized, the viewing angle dependence of the gamma characteristics is improved.
A liquid crystal display device disclosed in U.S. Pat. No. 8,952,877 is configured such that each pixel includes first and second subpixels, each of which has a subpixel electrode, similarly to the liquid crystal display device disclosed in Non-Patent Document 1, and a discharge capacitor (Cdown) is connected to the subpixel electrode of the second subpixel through a third TFT (corresponding to the TFT3 described above). Similarly to the case of Non-Patent Document 1, subpixel electrodes of the first and second subpixels are connected to data signal lines, which are different alternately for respective pixels, through first and second TFTs (corresponding to the TFT1 and the TFT2 described above), and two lines are simultaneously scanned. The control electrodes (gates) of the first and second TFTs are connected to a gate line (corresponding to the scanning signal line described above), and the control electrode of the third TFT is connected to a charge control line (corresponding to the discharge signal line described above).
In the liquid crystal display device disclosed in U.S. Pat. No. 8,952,877, for the two lines scanned simultaneously, gate lines are connected to each other through a gate connection line, and charge control lines are connected to each other through a charge connection line. Since these connections are made within the liquid crystal panel, the gate connection line and the charge connection line intersect with each other within the liquid crystal panel. The charge connection line is connected to a gate connection line for two lines scanned 1 H later than the above two lines. By such a connection, similarly to the liquid crystal display device disclosed in Non-Patent Document 1, a signal (corresponding to a discharge signal) delayed by 1 H from the scanning signal for each pixel is applied to the control electrode of the third TFT and the subpixel electrode of the second subpixel is connected to the discharge capacitor. As a result, the effective voltage applied to the liquid crystal layer by the second subpixel changes.
Incidentally, it is known that, in the TFT, due to the influence of the parasitic capacitance between the gate and the drain, a feed-through voltage (so-called pull-in voltage) is generated at the falling time of the driving voltage for the gate and the voltage of the drain (that is, the voltage of the subpixel electrode) drops. In addition to this phenomenon, due to the influence of another parasitic capacitance present between each subpixel electrode and the discharge signal line (or the charge control line), in particular, a phenomenon may be observed in which the voltage of the subpixel electrode of the first subpixel slightly rises and drops at the rising time and falling time of the discharge signal of the previous line.
For example, in a case where there is no signal overlap between the scanning signal and the discharge signal of the previous line, influences at the rising time and the falling time are appropriately canceled out in each subpixel electrode. For this reason, the above-described phenomenon is difficult to observe.